Messages in this thread | | | Date | Tue, 24 Oct 2023 14:43:30 +0000 | From | Benno Lossin <> | Subject | Re: [PATCH v2] rust: macros: improve `#[vtable]` documentation |
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On 24.10.23 13:24, Gary Guo wrote: > On Thu, 19 Oct 2023 17:15:53 +0000 > Benno Lossin <benno.lossin@proton.me> wrote:
[...]
>> -/// This attribute is intended to close the gap. Traits can be declared and >> -/// implemented with the `#[vtable]` attribute, and a `HAS_*` associated constant >> -/// will be generated for each method in the trait, indicating if the implementor >> -/// has overridden a method. >> +/// This attribute closes that gap. A trait can be annotated with the `#[vtable]` attribute. >> +/// Implementers of the trait will then also have to annotate the trait with `#[vtable]`. This >> +/// attribute generates a `HAS_*` associated constant bool for each method in the trait that is set >> +/// to true if the implementer has overridden the associated method. >> +/// >> +/// For a function to be optional, it must have a default implementation. But this default >> +/// implementation will never be executed, since these functions are exclusively called from >> +/// callbacks from the C side. This is because the vtable will have a `NULL` entry and the C side >> +/// will execute the default behavior. Since it is not maintainable to replicate the default >> +/// behavior in Rust, the default implementation should be: >> +/// >> +/// ```compile_fail >> +/// # use kernel::error::VTABLE_DEFAULT_ERROR; >> +/// kernel::build_error(VTABLE_DEFAULT_ERROR) > > Note that `build_error` function is considered impl detail and is > hidden.
I see, we should mention that in the docs on `build_error`.
> This should use the macro version instead: > > kernel::build_error!(VTABLE_DEFAULT_ERROR)
Is there a reason that it is a macro? Why is it re-exported in the kernel crate? The macro could just use `::bulid_error::build_error()`.
> Actually, the string here provides little use other than documentation,
Sure, but that is the whole purpose of this patch.
> since the string provided to build_error is only visible in const eval, > so this you might just omit that and write > > kernel::build_error!()
Note that it is also useful for people who read the code, as they can search for the constant and understand why it is a build error.
-- Cheers, Benno
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